Comparative study of synergistic inhibition of mild steel and pure iron by 1-hexadecylpyridinium chloride and bromide ions

[Display omitted] •The comparison of the corrosion behavior of mild steel and pure iron was studied.•HDPCl showed excellent protection for the mild steel corrosion but lower inhibition for pure iron.•Br− ion synergistically improved the inhibition performance of HDPCl due to the co-adsorption effect.•The adsorption of inhibitor systems on electrode surfaces followed Langmuir adsorption model. The comparison of the corrosion behavior of mild steel (MS) and pure iron (PI), and synergistic action of 1-Hexadecylpyridinium chloride (HDPCl) and Br− ion are studied in 0.5 M sulphuric acid solution. The study was carried out using open-circuit potential, potentiodynamic polarization, and electrochemical impedance spectroscopy measurements. In absence of inhibitor (blank), the corrosion rate of mild steel is greater than that of pure iron. In presence of HDPCl only, the inhibition efficiency for MS corrosion in H2SO4 is higher than that of PI and attributed to the different surface charges on both MS and PI in H2SO4 solution. The obtained results indicate that the inhibition efficiency (ηi%) of HDPCl is significantly increased in the presence of Br− ions for both MS and PI. In the presence of the Br− ions, the ηi increases significantly at relatively low concentrations of HDPCl ([HDPCl] = 8 × 10-6 M), i.e, ηi is 96 and 99% for MS and PI, respectively. The synergism factor (Sθ) is found to be more than unity suggesting greater ηi due to the addition of Br− ions to the HDPCl with a co-operative adsorption action. Chemisorption is postulated as the mode of adsorption based on extracted thermodynamic parameters.